Membrane proteins of biological tissues are insoluble in water, in salt solutions, or in other media in which most other proteins are soluble. Thus, other solvents have been developed for dissolution of membrane proteins. These solvents include aqueous solutions of detergents, dilute acid, aqueous solutions of protein perturbants such as urea, sodium hydroxide, etc., and aqueous solutions of chloral hydrate. However, these solvents are not optically transparent to ultraviolet radiation throughout the range of 200 to 400 nanometers (nm). Consequently, measurements of spectral properties of membrane proteins could not be obtained at these wavelengths. Such measurements are needed for estimations of protein concentrations from ultraviolet absorbances and of the amounts of secondary structures comprising protein conformations from ultraviolet circular dichroism.
We have now discovered a solvent system that not only dissolves certain membrane proteins but also is optically transparent to ultraviolet and visible radiation from 200 to 400 nm. By the method of the instant invention, a new mixed solvent consisting of about 4 parts ethanol, 1 parts acetonitrile and 1 part water is used to dissolve certain membrane protein. Although all ratios will yield an optically transparent solution not all ratios will dissolve the membrane protein. The absorbance and circular dichroic spectra of the resultant protein solution can then be examined throughout the electromagnetic wavelength range of 200 to 700 nm, but especially at ultraviolet radiation from 200 to 400 nm.